[Octree/Question] Accessing point indices/other contents of leaf/branch nodes at a specific depth

Your Environment

• Operating System and version: Mac OS Xcode IDE
• Compiler: GCC
• PCL Version:1.9.0

Context

I'm trying to build an octree to manage my point cloud data loaded from pcd file. I want to get the correspondent point indices in each voxel at a given depth of the octree...But I don't seem to find any method or example in the official documents.
I've tried to use FixedDepthIterator to traverse the tree and use "tree it.getLeafContainer().getPointIndices(vector)"something like this to get them.
But I don't know if I comprehend the usage properly and it's been a problem hard to solve before I can get the result and perform further study on region growth algorithms based on Octree.

Expected Behavior

Current Behavior

Code to Reproduce

This is the relevant codes I used after referring to the source codes of Class octreeViewer in Octree_viewer.cpp
void traverseOctree::getLeafNodesAtDepth(int depth){
//voxelCentercloud->clear();
pcl::PointXYZ pt_voxel_center;
vector point_idx_data;

for (pcl::octree::OctreePointCloudSearch<pcl::PointXYZ>::FixedDepthIterator tree_it = octree.fixed_depth_begin (depth);
     tree_it != octree.fixed_depth_end ();
     ++tree_it)
{

    // Compute the point at the center of the voxel which represents the current OctreeNode
    Eigen::Vector3f voxel_min, voxel_max;
    octree.getVoxelBounds (tree_it, voxel_min, voxel_max);
    
    pt_voxel_center.x = (voxel_min.x () + voxel_max.x ()) / 2.0f;
    pt_voxel_center.y = (voxel_min.y () + voxel_max.y ()) / 2.0f;
    pt_voxel_center.z = (voxel_min.z () + voxel_max.z ()) / 2.0f;
    voxelCentercloud->points.push_back (pt_voxel_center);
    voxelCenters.push_back(pt_voxel_center);
    cloud->points.push_back(pt_voxel_center);
   
    // If the asked depth is the depth of the octree, retrieve the centroid at this LeafNode
    if (octree.getTreeDepth () == (unsigned int) depth)
    {
      pcl::octree::OctreePointCloudVoxelCentroid<pcl::PointXYZ>::LeafNode* container = static_cast<pcl::octree::OctreePointCloudVoxelCentroid<pcl::PointXYZ>::LeafNode*> (tree_it.getCurrentOctreeNode ());
        tree_it.getLeafContainer().getPointIndices(point_idx_data);
    }
    // Else, compute the centroid of the LeafNode under the current BranchNode
    else
    {
      // Retrieve every centroid under the current BranchNode
      tree_it.getBranchContainer().getPointIndices(point_idx_data);
      pcl::octree::OctreeKey dummy_key;
      pcl::PointCloud<pcl::PointXYZ>::VectorType voxelCentroids;
    for(size_t i=0;i<point_idx_data.size();++i){
               cout<<" "<<point_idx_data[i]<<" "<<endl;
           }
}

}

Possible Solution

Start with Octree_viewer.cpp and the FixedDepthIterator usage shown in the issue. Read the iterator, leaf-container, and branch-container APIs to determine which contents can be retrieved at a requested depth. Done means the supported approach or limitation is documented with a minimal usage example.